Characteristics of the Mahdi
Shia sources
His name is generally accepted to be Muhammad bin Hassan-al-askari, just like Muhammad's full name. Mahdi is just a title. Muhammad literally means "praised one".
Some Muslims claim that his name can be an accepted variant of Muhammad such as Ahmed or Mahmoud; Supporters of this idea quote a passage from Muhammad in the Hadith which is interpreted: "If there remains only a day for the world to come to an end, Allah will prolong this day till He raises a man from my nation and my progeny. His name will be my name. He will fill the earth with justice and equity as it would have fraught with injustice and oppression." (Muntakhabul Asar by Lutfullah Safi Gulpaygani, p. 153)
His appearance is similar to that of Muhammad.
His character is like that of Muhammad, he would follow him perfectly and shall err not.
Walī al-‘Aṣr (Arabic: ولي العصر‎), meaning 'Guardian of the Era', is a title for the Mahdi.
Sunni sources :
He has a fair complexion.
He has a broad forehead and a prominent nose.
He will be from Ahl-ul-bayt (people of the household of Muhammad)*
Muhammad said: "al-Mahdi is one of us, the members of the household (Ahlul-Bayt)."
He will come from the East (i.e East of Arabian Peninsula).
His majority followers will be from a poor Nation from the East.
His majority followers will be from the Muslims belonging to the Lost
Tribes of Israel or the family of Prophet Ishaq living in the East.